In a variety of machine tools and other machinery applications, it is often critical to provide cantilevered supports for monitoring devices and the like which must be maintained at certain distances, and/or within predetermined tolerances relative to elements being monitored. For example, positioning scales and reader heads need precise mounting in order to accurately track positional changes of their respective support structures. For many sensitive monitoring devices, such as reader heads and scales, it is also imperative to minimize even momentary vibratory movements of the support arm assembly in order to prevent interruption of a dependable output signal train. The effectiveness of highly accurate monitoring and measuring devices can be drastically reduced or destroyed if supported in an unstable manner. Often such monitoring means are mounted on a machine part which is required to relatively move with respect to adjacent corresponding monitoring equipment. An example of such an arrangement would be a positional reader head which is attached for movement with a machine tool slide, and which must be consistently and reliably maintained in substantially vibration-free, close spacing with a monitoring scale attached to the machine tool slideway.
While damping of vibrations in machine tools or other machinery has been provided in a variety of ways over the years, many instability problems must be handled on a case by case basis, and reliable and simple solutions remain elusive in many circumstances. For example, a tuned vibration damper assembly for machine tools is shown in U.S. Pat. No. 3,522,864, which issued to R. C. Richter. Particularly, this patent shows the use of a tuned damping structure for eliminating vibrations in a rocking grinder wheel head arrangement, and contemplates the provision of its assembly on an angular face of the machine tool. A damper mass is connected to the machine tool on at least one viscoelastic damping element via a resilient bolt and spring assembly. Modal analysis of the machine tool geometry is used to determine the mounting angle of the damper mass in order to attenuate the horizontal and vertical components of the unwanted vibration in the tool. Conventional teachings in the industry also lead one to overcome vibrational problems of support structures by designing the structure as statically stiff as possible, and/or by hanging additional mass in strategic arrangements, such as shown in Richter ' 864. It has been found, however, that in applications where the machine tool arrangement is already relatively stiff, such conventional techniques are not always effective in addressing vibrational instabilities.
Other applications in the prior art in which damped structures have been successfully applied in machine tool environments include the tool turret shown in U.S. Pat. No. 4,491,044, which issued to R. G. Haas, et al. Particularly, Haas et al. teach the application of a squeeze-film damper to a cantilevered tool, wherein the tool extends from the face of a large plate which is attached about its inner edge to a machine base. A film damping chamber of relatively large cross-sectional area is created adjacent the bolt circle and sealed by a plurality of O-rings to provide a closed damping chamber between the spindle end face and the adjacent tool support plate. An oil film damper is also described in U.S. Pat. No. 4,764,033, which issued to Mark Kohring and Ed Bailey. Particularly, the '033 patent shows the provision of a rotator bearing shock and vibration dampener wherein a relatively thin oil damp well space is provided below the outer race of a turntable bearing and provided with limited inlets and outlets. The oil film tends to resist displacement thereby dampening vibrations and mechanical shocks often encountered in a robotic manipulator turntable bearing in use.
Another bearing mount utilizing a squeeze-film damping arrangement is shown in U.S. Pat. No. 4,509,804, which issued to S. Klusman. The Klusman bearing mount contemplates the use of a tubular bracket within which a high speed rotating shaft is to be housed, with one end of the bracket bolted to a base member within which a film damping chamber is provided. Radial deflection of the bracket housing manifests itself in the diaphragm spring portion of the tubular housing, causing local collapse of the squeeze-film chamber. The rotating shaft is thereby maintained in a concentric relationship with the central axis as a result of the resilient bracket. Other damping arrangements for reducing vibrational instabilities of cantilevered tools can be seen in U.S. Pat. Nos. 3,499,350 and 3,499,351. These patents pertain to the use of a viscous damper and a viscoelastic damper, respectively, applied to a cantilevered tool via a damper bar which extends from the tool base in a direction opposite to that of the tool and into a damping chamber.
While many of the above-referenced prior art teachings have been successfully employed in various machine tool applications and the like, most have been specifically designed for overcoming somewhat limited and particular problems in custom applications. Some of these structures, however, such as the Klusman bearing mount arrangement, are relatively complex, and, therefore, less preferred, especially for less complex and non-rotating situations. Consequently, heretofore there has remained a need for providing a simple yet widely adaptable damping assembly which can be used in a variety of cantilevered support arm assemblies without unduly complicating the structure and without substantially constraining performance of a machine tool monitoring device or the like.